The long term objective is to understand the nature and limitations of the biological response to nerve injury in the taste system. Which properties of sensory end organs depend on innervation, and what factors are necessary for regeneration of normal end organs? Is functional recovery possible; and are central nervous system changes involved? Taste bud (TB) receptor cells have short lifetimes and their renewal is thought to depend on innervation since denervated TBs atrophy. TBs innervated by the glossopharyngeal nerve apparently disappear after denervation. However, recent evidence shows that fungiform TBs, which are normally innervated by the chorda tympani, persist in an dedifferentiated state as remnant cells for months without innervation. The rapid reappearance of normal TBs after reinnervation of the epithelium, suggests that the constituent cells are derived from remnant TB cells. In order to understand the role of the remnant buds, it is important to fully characterize them, to determine how they differ from normal TBs, and to describe the process of reinnervation and reappearance of normal TBs. Morphology, cell turnover, and antigenic properties of normal, chronically denervated, and regenerating fungiform TBs will be studied in hamsters. The structure of the TBs will be revealed with three dimensional reconstructions of TBs made with the aid of high voltage electron microscopy (HVEM). Cell turnover will be addressed by pulse labeling of DNA with tritiated thymidine in combination with HVEM. Antigenic properties will be identified with monoclonal antibodies known to bind to normal TB cells. Little is known about functional recovery of the taste system following nerve section or injury. In humans, damage to the chorda tympani frequently results from surgery (eg. for otosclerosis) or disease (eg. Bell's Palsy). Recovery of chorda tympani mediated taste function will be ascertained by recording the response of single units in the regenerated nerve, and be determining the recovery of a taste related behavior dependent on the chorda tympani nerve; a conditioned aversion to sodium salts.